1. Field of the Invention
The present invention relates generally to nebulizers and nozzles for use in analytical spectrometry and fuel spray technology (for example, fuel injector systems, inhalers, and the like). More specifically the present invention relates to smart nozzles and nebulizers that can be adjusted to produce an aerosol with optimum and reproducible quality based on the feedback information provided by a laser imaging technique. (Throughout the specification the terms “droplets”, “aerosol” and “particles” may be used interchangeably.)
2. Description of the Related Art
In flame and plasma spectrometry, test solutions are typically introduced into the flame or plasma in the form of a liquid aerosol. The bulk liquid is first converted to a spray, usually by means of a pneumatic nebulizer. The aerosol is then conditioned by removing the larger droplets with a spray chamber before introduction to the plasma. The spray chamber suffers from large memory effects, signal broadening during chromatographic separations, volatile analyte loss, and transient acid effects. Alternatively, direct sample introduction can eliminate such shortcomings. Nevertheless, the quality of the aerosol produced, for example by inductively coupled plasma (ICP) nebulizers, greatly affects the analytical performance of the technique in both direct and indirect sample introduction. For example, the properties of sprays affect the performance of combustion devices in jet engines, drug delivery from dose inhalers, and distribution of chemical supplements in agricultural applications.
Introduction of samples into the plasma remains the main problem in inductively coupled plasma mass spectrometry (ICPMS)1 and atomic emission spectroscopy (ICPAES)2 despite recent improvements in the analytical performance indices.3-9 Aerosol characterization and nebulizer diagnostics offer valuable information on the fundamental aspects of sample introduction in plasma spectrometries and confirm models for aerosol generation and transport.10-16 Droplet size and velocity distributions are the most important factors that determine the quality of an aerosol. Small and monodisperse droplets, with low and uniform velocity, must be introduced into the central channel of the plasma for efficient desolvation, vaporization, atomization, excitation, and ionization of the sample.17-21 
Various techniques have been utilized for the determination of average size and size distribution of the droplets produced by ICP nebulizers, with the optical approaches being preferred to mechanical methods because of their non-intrusive nature and greater accuracy.4,5,22 Lorenz-Mie scattering,23 phase-Doppler particle analysis (PDPA),5,17,19 and laser Fraunhofer diffraction24-28 are among the most popular optical techniques for droplet size measurements in ICP nebulizers. A recent method introduces a novel aerosol diagnostics technique, which unlike point measurement methods, provides spatially-resolved three-dimensional (3-D) particle size and mass distributions for ICP nebulizers by acquiring 2-D maps at several distances from the nozzle.29,30 
Among cited techniques, only PDPA measures the velocity of the droplets at points within the spray field. Importantly, except for a few reports,17,19,31-33 no in-depth study has been published on the velocity distribution of the aerosol produced by ICP nebulizers. Nevertheless, the velocity of droplets is one of the most important factors in the desolvation, vaporization, atomization, excitation, and ionization of the analyte. High velocity droplets experience shorter residence times and consequently less particle-plasma interaction compared to slow droplets. Furthermore, the studies conducted so far have provided only single-point measurements.